For critics of early Christianity, one of the stock objections is that Jesus predicted he would return in the lifetime of his disciples. And since he clearly didn’t return, then he cannot be believed.
Indeed, it is this belief that has spurred many other theories among scholars, most notably Hans Conzelmann’s thesis that Luke’s Gospel was written to explain the delay of the second coming.
But, is it really true that Jesus predicted that he would return in the lifetime of his disciples? Here’s a recent video where I briefly address this question:
As for whether the imminent coming of Jesus affected the development of the NT canon, see my other article here.